1. Field of the Invention
The present invention relates generally to a communication system including a plurality of sensor nodes. More specifically, the present invention relates to a method for seamlessly transmitting information collected at sensor nodes to a client.
2. Description of the Related Art
Recently, the computing environment has been advancing toward a ubiquitous computing environment with the rapid prevalence of Internet and mobile networks and the convergence of wireless networks. The advent of new nodes and services has brought a trend toward compactness and intelligence. Especially, intelligent services are provided in association with context information of users.
The context information collected by the nodes is present in the service environment and provides information for efficient services, including behavior, location, direction, and environment conditions of the user. To deliver the intelligent service suitable for the environment of the user based on the context information, it is required to aggregate, store, classify, translate, and combine the context information. In addition, standardization is demanded for predictable context information so as to take advantage of various types of context information.
Given the widespread prevalence of the mobile computing environment, nodes need to rapidly adapt to the ever-changing environment. In other words, the services in such an environment require the discovery of a device (node) to provide the context information and to obtain the context information. In this regard, architectures that support service discovery protocols such as Jini, Service Location Protocol (SLP), and Salutation are available.
FIG. 1 illustrates a communication network constructed with a plurality of sensor nodes. The communication network includes an access point (AP) 102 and a client 100. The client 100 discovers sensor nodes that provide the context information and request the context information from the sensor nodes. The sensor nodes are randomly located within a sensor field 110. The sensor nodes collect the context information according to the request from the client 100. When the client 100 requests at least two context information, the sensor nodes transfer the two context information as requested. The AP 102 relays messages (packets) between the client 100 and the sensor nodes.
FIG. 2 illustrates how to transmit and receive the context information according to the request of a client in a communication network including a plurality of sensor nodes, which will be explained below.
Referring to FIG. 2, the communication network includes a client, an AP, and a sensor node 1 through a sensor node N. It should be understood that the communication network may include other components besides those mentioned above. Note that FIG. 2 illustrates only requisite components to facilitate the understanding of the present invention.
The client transmits a discovery request packet to the AP to obtain context information requested from a user (S200). The discovery request packet contains the context information requested from the user and information relating to an address of the client. Even when the user requests at least two context information, the client can transfer only one discovery request packet to request the context information.
Upon receiving the discovery request packet, the AP forwards the discovery request packet to neighbor sensor nodes (S202). The AP duplicates the received discovery request packet and consecutively forwards the duplicate packets to the neighbor sensor nodes. Typically, the AP forwards the duplicate packets to the sensor nodes within a short time period. It is noted that the AP can multicast the received discovery request packet to the neighbor sensor nodes without packet duplication.
The sensor nodes, upon receiving the discovery request packet, collect the context information requested by the user. If the user requests at least two context information, the sensor nodes collect the at least two context information respectively.
After collecting the context information, the sensor nodes transmit a discovery reply packet to the AP (S204). Although FIG. 2 depicts that the sensor node 1 through the sensor node N send the discovery reply packet to the AP at the same time, the sensor node 1 through the sensor node N collect the requested context information, generate the discovery reply packet containing the collected context information, and then transmit the generated discovery reply packet to the AP. Accordingly, the sensor node 1 through the sensor node N may transmit the discovery reply packet to the AP with a time difference.
The sensor node 1 through the sensor node N receive the discovery request packet from the AP and collect the context information substantially at the same time. Thus, the sensor node 1 through the sensor node N transmit the discovery reply packet to the AP substantially at the same time.
The AP forwards the discovery reply packet received from the sensor node 1 through the sensor node N, to the client (S206). When the discovery reply packets are received from the sensor node 1 through the sensor node N at the same time, the AP is not able to process all the received packets. Thus, the AP temporarily stores some of the packets in queue. The packets in part are temporarily stored in the queue since the AP cannot forward all of the received packets to the client. The packets beyond the storage capacity of the queue are lost or dropped. The greater the number of sensor nodes in the communication network, the greater the number of discovery reply packets received at the AP. Therefore, the packet drop ratio increases.
The client, which does not receive some of the discovery reply packets, retransmits the discovery request packet to the AP for more accurate context aggregation. Upon receiving the discovery request packet retransmitted from the AP, the sensor nodes retransmit the collected context information. As a result, the total discovery time and the network traffic increase in proportion to the number of the retransmissions.